Meteorological Mexican wave threatening busy end to 2021 season.
A number of addressees have advised us that they have not received our bulletins for 2-3 days. This would appear to be due to a technical glitch, for which experts sometimes use the term ‘progress’. Fortunately, there have been no pressure gradients of any significance and those who have received our emails without interruption have been standing easy.
Today, Disturbance Fifty Six is 450 miles north of the mouth of the Amazon, bimbling along happily at 14 knots. Despite some signs of rotation and some heavy thunderstorm activity, upper level shear rules the day. Aside from showers and thunderstorms over the south-eastern Caribbean overnight on Wednesday, this is not likely to bother anyone.
More addressees are asking if this prolonged halt in storm production in such a busy year is indicative of the end of the season drawing near. If it is were only for the sterling work of upper level wind shear throttling anything with vertical convection, I would be pleased to say yes. No hurricane has reached U.S. soil since September 14th and not a single tropical storm has piped up in the Atlantic Basin since October 6th – apparently the longest such dry run in eight years – despite plentiful above normal sea surface temperatures and rising air continuing to attempt convection cycles forming across the reporting region.
I have tried to limit the amount of jargon, which along with the antics of the Canadian Guy, has long been a popular feature of these reports but now, in the middle of my fourteenth reporting year, it is with a heavy heart that I have to discuss Madden-Julian Oscillation. This is best compared with a sort of global Mexican wave of unsettled pressure gradients which can begin at one side of the arena and later blight the other side where irritated sports fans are trying to watch the game without having milkshake thrown over them. As an example, hurricane experts consider that a series of disturbances in the Indian Ocean in July set up the Atlantic Basin for an active August when, as we know, seven named storms developed between 11th and 31st August. Three of those grew into major storms including IDA of course, which hit a recorded gust of 150 knots.
During the last month, the oscillation’s state became less favourable for promoting Atlantic storms but this is running out and it now seems may favour a flurry of late season developments on our side of the arena. I wouldn’t normally hang my hat on this. The Madden-Julian Oscillation idea is great on paper but has its drawbacks. No one is certain why it forms in the first place, forecasts of its movements are imprecise and there are significant movements across the globe which are not driven by this, indeed some years go by without any Madden-Julian Oscillation activity at all. Nonetheless, the science wonks have highlighted this so it should not be ignored completely and observers would be well-advised to hang on to their hotdogs.
Enough jargon. Warm water and rising air, with a late developing La Niña cooling of surface waters in the tropical Pacific likely to dampen the spirits of upper level shear, lends support to some of the more reliable modellers who are predicting significant late activity before the season ends.
For now at least, stand easy.
Image Kyōko Aizome